It is frequently necessary to embed metal inserts in work pieces formed of metal, plastic or other material in order to mount threaded or other elements thereon. For this purpose it has been suggested that the metal insert be formed with a sleeve portion and a nut portion arranged so that the nut portion may be drawn into the sleeve portion so as to expand the sleeve portion and force it outward into engagement with the side walls of the opening or cavity in which the insert is positioned. Typical devices of this type are disclosed in U.S. Pat. Nos. 1,808,318; 3,216,304; 3,411,398; 3,493,254 and 3,566,739. However such constructions require the opening in which the insert is to be embedded to pass all the way through the work piece or to be of greater depth than the insert. As a result, the base of the nut portion of the insert is unsupported and is only held in place by frictional engagement of the nut portion with the sleeve portion. Accordingly the nut portion is capable of end play and may be separated from the sleeve portion of the insert in the event a bolt or the like threaded into the nut portion is subjected to axial forces such as a blow tending to separate the nut portion from the sleeve portion. It is further found that radial expansion of the sleeve portion of the insert tends to rupture the sleeve so as to weaken the sleeve and the retention thereof by the nut portion and by the work piece.
In accordance with the present invention the insert embodies a sleeve portion and a nut portion initially joined by a frangible connection permitting the sleeve portion to be forced downward about the nut portion into telescopic relation therewith while the nut portion remains in engagement with the bottom of the cavity in which the insert is positioned. The sleeve portion of the insert is provided with inclined splines on the exterior thereof adapted to dig into the side walls of the cavity causing it to rotate as it is forced downward into the work piece and over the nut portion of the insert. In this way the sleeve portion is caused to spin or rotate and is subjected to metal working or swaging action as it enters the cavity in the work piece threading its way into position while being expanded by the nut portion of the insert. At the same time the nut portion is forced against the bottom of the cavity so as to be held against rotation as the sleeve is rotated with respect thereto.
Such working of the metal of the sleeve is found to markedly reduce the tendency of the sleeve to rupture as it is expanded by the nut portion. As a result the sleeve portion is positively connected to the work piece in a manner which effectively resists axial movement of the sleeve portion with respect to the work piece. In a similar way the nut portion of the insert also is provided with outwardly projecting ribs which dig into the inner surface of the sleeve portion as it moves into telescoping relation therewith. In this way the working and rotational movement of the sleeve is aided during insertion thereof into the work piece whereas relative movement of the nut portion and sleeve portion after insertion is prevented and a positive connection between these two elements is established. As a further feature of the present invention the nut portion of the assembly is provided with a zone of reduced diameter near the end thereof so that after the sleeve portion has moved downward past the zone of maximum diameter of the nut portion the expanded sleeve portion will contract inward so as to embrace the nut portion effectively and lock the nut portion and sleeve portion together as a unit further preventing axial separation or displacement thereof with respect to each other.